Mapping the thickness of retinal layers using Spectralis spectral domain optical coherence tomography in Indian eyes

Abstract

Purpose: This study aimed at establishing the normative data for the thickness of macular layers on Spectralis Spectral-domain optical coherence tomography (SD-OCT) in healthy Indian eyes and testing the effects of age, gender, central corneal thickness (CCT), and intraocular pressure (IOP) on such values.

Methods: This cross-sectional study was done on 308 eyes of 159 healthy subjects. OCT scans were obtained using the posterior pole asymmetry scan protocol. From the thickness map, data were grouped into nine Early Treatment Diabetic Retinopathy Study (ETDRS) macular sectors. Correlation between retinal thickness and age/IOP/CCT was done using Pearson correlation. Correcting for age as a covariate, multivariate regression analysis was done to know which retinal layers showed significant differences in thickness between males and females.

Results: The mean age was 46.06 ± 13.06 years (range: 20-75 years). Significant central subfield (CSF) thickening with age was noted in retinal nerve fiber layer (RNFL), inner nuclear layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), and outer nuclear layer (ONL) (P < 0.04). The average thickness of the outer ring reduced with age in the ganglion cell layer (GCL)/IPL/INL (P = 0.001). Women had thinner inner and outer retinal thickness than men in all ETDRS rings (P < 0.001). There was no interocular asymmetry (P > 0.05) and no correlation between IOP/CCT and retinal layer thickness.

Conclusion: In CSF, age-related thickening was noted in RNFL, IPL, INL, OPL, and ONL. The average inner ring thickness decreased with age in GCL and IPL and increased in the RPE layer. The average outer ring thickness decreased with age in GCL, IPL, and INL layers and increased in OPL. The average IR and OR thickness was significantly less in women compared to men in all sub-fields. There was no correlation between IOP/CCT and retinal layer thickness.

Keywords: Age; gender; macular layers; normative; optical coherence tomography; thickness.

Figure 1

(a) HRA image showing the extent of the macular area scanned in the posterior pole asymmetry protocol and the ETDRS grid (Central subfield: 1 mm, Inner ring [composed of four subfields between 1 and 3 mm distant from the center], and Outer ring [composed of four subfields between 3 and 6 mm distant from the center]). (b) OCT image showing layer-wise extents: RNFL (from the internal limiting membrane [ILM] to RNFL), GCL (from RNFL to GCL), IPL (from GCL to IPL), INL (from IPL to INL), OPL (from ONL to OPL), ONL (from OPL to the external limiting membrane), RPE (from upper RPE to Bruch’s membrane), IR (from RNFL to ONL), OR (photoreceptors and RPE) and TR (all retinal layers)

Figure 2

Scatterplots of simple linear regression between age (x-axis) and the thickness of different retinal layers (y-axis). (c: Central sub-field, Avg-O: Average thickness values from the outer ring of the ETDRS grid [composed of four subfields between 3 and 6 mm distant from the center], Avg-I: Average thickness values from the inner ring [composed of four subfields with a distance between 1 and 3 mm from the center], Total retinal thickness (TRT), Retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), Inner nuclear layer (INL), Outer plexiform layer (OPL), Outer nuclear layer (ONL), retina pigment epithelium (RPE), Inner retina (IR), Outer retina (OR), micrometre (µm), # indicates P < 0.05)